Science and Truth

There’s one rather cynical way of looking at science that goes something like this: everything in science eventually turns out to be wrong.

You can understand where such thoughts originate. Once, the best scientists in the world told us that space and time were separate. Then along came Einstein to show how they were linked. Scientists once thought that continents had always existed right where they are today. Then Eugene Wegener showed that continents drift across the globe. Once we thought atoms were indivisible. Then along came a whole zoo of particles that stream out of atoms every time we hit them hard enough. Maybe, this line of thought goes, science just describes what we can see today. When we can see more (with better telescopes, better microscopes, and so on), science will tell us something totally different.

I want to show you why that’s not true. Truth really is out there, and science really is getting at it. Here’s the story.

In 1930, a scientist named Wolfgang Pauli had a big problem. He knew that a particular property of some radioactive elements, called beta decay, didn’t make sense. Somehow, in beta decay (unlike any other process we’d ever studied) energy was disappearing. The idea of conservation of energy is a deep one in science, so Pauli and other scientists were eager to preserve it. To make the math come out right, Pauli invented a new thing, called a neutrino, that would fly out of a beta decay, completely undetected.

Since no one had ever seen a neutrino, many scientists doubted that such an invention was really science. It seemed like an ugly patch to prop up a failing theory. Still, conservation of energy was so important that many scientists went along with this idea of an object that no one could detect.

Fast forward to 1956. Scientists had realized that if beta decay made neutrinos, these neutrinos might occasionally be captured in a sort of reverse beta decay. Just as it’s a lot harder to catch a baseball than to throw one, it would be a lot harder to capture a neutrino than to send one flying. But two scientists named Clyde Cowan and Frederick Reines were ready to try catching neutrinos.

Cowan and Reines built their neutrino trap from 200 liters of water. They placed it just outside a nuclear reactor. Every hour, of the billion trillion neutrinos predicted to pass through their water tanks, Cowan and Reines captured three. But these three events per hour were enough to prove that neutrinos, Pauli’s “made-up” particles, were real. Scientists really were on to something.

Today, neutrinos are crucial scientific tools. Because they almost never react with anything, neutrinos can pass through matter effortlessly. An ordinary piece of light (called a “photon”) takes thirty thousand years to emerge from the center of the Sun, but a neutrino flies through the Sun in seconds. Neutrinos also pass through the entire Earth, so that every night enormous numbers of neutrinos from the Sun emerge from your floor and fly through your body as if you weren’t even there.

But every once in a while, quite by accident, one of those neutrinos collides with an atom. Nestled deep in the Japanese Alps is a very special telescope called the Super-Kamiokande neutrino detector. This telescope doesn’t look up at the sky. Instead it looks down, searching for neutrinos that have passed all the way through the Earth. Instead of 200 liters of water to trap neutrinos, Super-K contains around 45 million liters. When a neutrino collides with one atom in that water, scientists at the Super-K can tell exactly where that neutrino came from. This picture of our Sun was taken by the Super-Kamiokande telescope over the course of many, many nights, as its enormous water pools detected one solar neutrino after another.

Look closely at this picture. It is evidence that science is not just a description of the world. It is a search for truth, a search for things that are actually there. And it’s a search that is getting somewhere. Neutrinos, those objects invented just to make the math come out right, really do exist. And we humans, using first our brains and then our technology, have found them.